This invention relates to aircraft which can take-off and land vertically (VTOL aircraft) and aircraft having a short take-off and landing capability (STOL aircraft). The invention is particularly concerned with VTOL and STOL aircraft that are also equipped with a lift augmented wing (hereinafter called an augmentor wing).
By "augmentor wing" it is meant a wing of the type in which pressurised air is blown through openings in the wing to induce an air flow over the lift developing surfaces of the wing. The air which is induced to flow over the wing augments the lift and such a wing is useful when the forward speed of the aircraft is low.
A well known example of a fixed wing aircraft having an augmentor wing is the De Havilland of Canada aircraft known as the Buffalo.
The present invention is relevant to a fixed wing aircraft or to helicopters
In our co-pending British Patent Application No. 8234318 there is disclosed a helicopter which includes a gas turbine engine having a core gas generator, a power turbine driven by the exhaust of the gas generator and connected to drive the helicopter main lifting rotor, and a variable area final propulsion nozzle for controlling the power to the rotor. This application corresponds to U.S. patent application Ser. No. 555,090, filed Nov. 25, 1983. A compressor of the engine is used to supply pressurised air to an augmentor wing. By varying the area of the propulsion nozzle, it is possible to reduce the power to the main lifting rotor and simultaneously increase the forward thrust which is developed by the engine as a turbo jet reaction. Hence it will be possible to achieve very high forward speeds than currently attainable and operate the helicopter in a mode where the main lift is developed by the wings and not by the lifting rotor.
One of the problems envisaged with such a compound helicopter is that of decelerating the forward speed of the helicopter. At very high speeds it will be impractical to tilt the rotor or pitch the nose of the helicopter upwards in the conventional way because the aerodynamic loads on the main lifting rotor would be too high. In any case, even at lower speeds, when the majority of lift is taken by the main rotor, it would be undesirable to pitch the nose of the helicopter upwards. To do so would expose the underside of the helicopter to the ground fire of an enemy position and obscure the pilot's view of the enemy positions. The pilot would also be unable to aim his armaments at the enemy ground positions until a horizontal attitude had been regained.
There is, therefore, a need to be able to decelerate the helicopter without having to rely on conventional methods and at the same time enable the helicopter to assume a level attitude.
Although the primary object is to provide a means of decelerating helicopters that are equipped with a blown augmentor wing, it is also relevant to decelerating fixed wing aircraft which have an augmentor wing.
The invention as claimed uses the flaps that are provided as part of the augmentor wing and enables these flaps to be moved into the ambient airstream and thereby decelerate the aircraft.